Dell has posted a page extolling the virtues of Linux (Ubuntu in particular), with a quick explanation of what Linux is and how it compares against Windows. Of course, the page links off to Dell's various computers that ship with Linux pre-installed.

I can see the logic in there, because 9.04 is a much more polished release than 9.10 (which included a pulseaudio update which broke sound again on VIA chips and crappy wi-fi performance on Atheros chipsets) and 10.04 (which includes a puzzling windows button positioning which makes getting used to the OS harder for no reason, and the introduction of Plymouth while the technology still can't exactly be called bullet-proof). They probably wait to see what 10.10 looks like before upgrading to one of those three ones.